1. Field of the Invention
This invention relates to antenna radiation pattern measuring equipment and more particularly to low-distortion positioning equipment for antenna radiation pattern measurements.
2. Description of the Related Art
To completely characterize an antenna radiation pattern--especially for antennas having low gain and broad beamwidth--the gain must be measured over the entire 4.pi. steradians solid angle. There are three ways to accomplish this goal. One way is to hold the antenna under test (AUT) in place and move the probe antenna along the surface of an imaginary sphere at a fixed radius from the AUT. The apparatus used to move the probe antenna is usually unwieldy and causes unwanted scattering which distorts the AUT radiation pattern.
A second way to accomplish the goal is to hold the probe antenna stationary and rotate the AUT such that the probe antenna appears to move along the imaginary sphere with respect to the AUT. The AUT orientation is changed at a fixed point thereby reducing the size and complexity of the positioning equipment compared to the first way. This is probably the most usual configuration. The positioning equipment once again causes undesired scattering that distorts the radiation pattern of the AUT.
The third way to accomplish the goal is to combine the previous two techniques. Usually the AUT is rotated azimuthally while the probe antenna is moved along an arc above the AUT. The concept is simpler than either of the two previous techniques, but the distortion caused by the positioning equipment is usually significant. To reduce the complexity of the arc and the azimuth rotator, the arc is usually incomplete--a portion of the radiation pattern is purposely excluded from the measurement. Depending on the shape of the radiation pattern, this can be a serious problem.